The present invention relates in general to fluid sampling of zones in wells intersected by fractures and in long-screen wells in unconsolidated aquifers.
The GroundWater Protection Council (1999) indicates that thousands of waste disposal sites are present in the northeastern United States where fractured-rock aquifers predominate. Innovative sampling systems that can effectively and efficiently sample fluids in heterogeneous aquifers are particularly relevant in helping to identify contaminant distribution and pathways.
Fluid sampling in open boreholes tapping fractured-rock aquifers is particularly challenging because of vertical mixing of fluid within the borehole from flow from multiple fractures. The use of downhole pumps to pump water or other fluid from long, open-hole bedrock wells or long-screen sections of wells is problematic because the well bore acts as a conduit and induces vertical flow and mixing of fluid from multiple fractures at different zones (depths) throughout the entire well opening based on the transmissivity of each fracture (Shapiro, 2002). The source of the pumped fluid in an open borehole is a mixture of the well bore fluid and the flow-weighted contribution of fluid from multiple fractures. The unknown source origin of the resultant fluid sample is less than ideal for the identification of natural and anthropogenic contaminant pathways.
Packers that straddle the pumps have been used to isolate flow from discrete fractures or fracture sets to reduce capture of well bore fluid (Shapiro, 2002). However, the use of packers can be time consuming and logistically difficult. An easier and more efficient sampling system is needed.